im rebuilding a 1275 midget engine, fitted the mains with new shells etc as I tighten the main bearing bolts the lock tabs seem to turn with the bolt and get all chewed up and bent. Ive tried this twice now, same thing happened each time

Ive read on the minispares website that some of the A+ engines were not fitted with locktabs (although the midget engine is not A+) are they really needed to prevent the bolts loosening?
Picky
1969 Four door Saloon Old English White 1275 with ported head and HS4 carb. Wolseley 1500 front brakes. Currently off the road with a leaky master cylinder!